The present invention relates generally to a synchronous compression and reconstruction system for video and audio data. More specifically, the invention relates to a synchronous compressive recording system for recording video and audio data through compression process with establishing synchronization therebetween, on a recording medium, such as a CD-ROM, hard disk and so forth, and further to a synchronous reconstruction system for synchronously reconstructing video and audio data from the recording medium, on which the data is recorded through a data compression process, or through a telecommunication circuit.
In the recent years, on-line data retrieval systems have been progressively spreading. Through such online data retrieval systems, video and audio data demanded by users can be retrieved by establishing a database for preliminarily recording video data and/or audio data in a large capacity recording medium, such as CD-ROM, hard disk or so forth and by permitting the user to access the database through a telecommunication circuit from a terminal.
In such case, the video and audio data are basically analog data. Therefore, it becomes necessary to perform digital conversion for such data for recording on the recording medium. However, when digital conversion is performed for these analog data, the amount of data becomes much greater than character data. Therefore, various data compression technologies are employed for the video signals and audio signals for recording the large amount of data on the recording medium. Electronic data file systems which can record and retrieve such data have been put into field use.
An example of such system is a multi-media computer system which performs a video and audio signal compressing process according to an image coding method in conformance with ISO10918-1 (JPEG: Joint Photographic Expert Group). In this compression system, compression of an image is generally performed by dividing one frame into 8.times.8 blocks, and performing discrete cosine transformation (DCT), quantization and entropy coding, respectively per block. Also, reconstruction of the compressed image is performed by performing respective entropy decoding, reverse quantization and reverse DCT for each block of 8.times.8 blocks.
For such system, an apparatus which can perform high speed edition, compression and recording on the recording medium for a large amount of data of video and/or audio and so forth, is required. Also, when reconstructing audio data in combination with the corresponding video data, matching the reconstruction of the audio and video data (synchronization) becomes necessary. Particularly, due to the performance of the apparatus or size of compressed code of the video image, the recording and reconstructing speed of the video data can be lower than the recording and reconstructing speed of the audio data so that synchronization cannot be established between the video data and audio data upon reconstruction. As a result, the perceived video and audio signals seem unnatural.
Prior art for establishing synchronization have been disclosed in Japanese Unexamined Patent Publication (Kokai) No. 63-168745, Japanese Unexamined Patent Publication No. 63-266579 and Japanese Unexamined Patent Publication No. 63-313384. These conventional synchronization systems will be briefly discussed hereinafter. In the process of data compressive transformation of a large amount of video and audio data, a data file is established for attributes of the data, such as data type, data length, data conversion method, associated data to be synchronized and so forth. These data files are stored as a data control file. Thereafter, using the data file stored in the data control file, so-called simulated reconstruction in a form assuming reconstruction of data recording in a final form of a recording medium is performed. At this time, real time reconstruction of the audio signal, combination of the image and voice, matching quality of reconstruction timings and so forth are checked by eye and ear:
At this time, reconstruction is performed on the basis of the content of data file in a control file, and the process of simulated reconstruction is modified to freely set the timing or so forth when the synchronization between the image and voice is not established. By such simulated reconstruction, operation is checked and adjusted to generate an edited program file.
In such a video/audio synchronization system in the conventional video and audio compressive reconstruction system, drawbacks are encountered in that the data file must be generated for matching the timing, and the simulated reconstruction on the basis of the content of the data file and checking the operation have to be repeated. According, such work is time consuming.
Also, in another conventional video and audio synchronization system, digital codings of the video data and the audio data are performed by mutually independent equipment. Then, the video data and the audio data are correlated according to a given format, transmitted or accumulated, and reproduced by independent decoders for the video data and the audio data after separating the video and audio data again. As a method for realizing coincidence between the video data and the audio data, a method for providing a reconstruction format generated by predicting the delay magnitude between the video data and the audio data in each individual reconstruction system for coupling the video and audio data for simultaneous reconstruction is employed. Alternatively, a method for providing an "output delay circuit" for the reconstruction system and adjusting the delay magnitude of a subject dynamic image, is employed.
For example, Japanese Unexamined Patent Publication No. 3-150552, for "Video and Audio Editing System" discloses a synchronization method for editing the audio data recording on a magnetic tape through digital conversion therefor, with respect to a video film (primarily a movie or so forth). In the disclosed method, after performing patching work for the audio data according to address data included in the magnetic film, reconstruction is performed employing an editing magnetic tape capable of perforation synchronous driving with the video film. Namely, synchronization of the system is realized by hardware, which functions satisfactory with a sufficient preliminary adjustment.
Furthermore, an editing means disclosed in the last-identified publication is provided with means which is described as "having a function to modify only length without causing variation of tone of the voice" as a measure for the case where "words finish earlier than pictures" possibly caused after the recording of "words", so that output image and voice are checked by human eye and ear to make correction with one or more operations.
In the above-mentioned conventional video and audio synchronization system, since the amount of data to be generated varies depending upon the nature of the subject image, (i.e. due to the complexity of the picture or magnitude of action, the picture fluctuates per unit for coding so that the period required for decoding reconstruction of the image cannot be determined unitarily, synchronization is not performed initially. Then, measure is taken to predict a delay magnitude as a typical value to process all data with a uniform reference, or, as in the editing operation of movie, after checking the deviation of the magnitude of delay between the image and the voice upon reconstruction through actual reconstruction, prediction of the delay magnitude between the image and voice is performed again for coupling in order to obtain coincidence. Therefore, it is not possible to correct the delay magnitude between the image and the voice in a method adapted to a condition in real time for precisely maintaining synchronization between the image and voice upon reconstruction. This may cause problems of interruption of a sequentially reproduced voice, variation of tone and so forth.